
(define nil '())

(define (element-of-list? x xs is-eq?)
  (cond ((null? xs) #f)
        ((is-eq? x (car xs)) #t)
        (else (element-of-list? x (cdr xs) is-eq?))))

(define (element-of-sorted? x xs is-eq? is-less?)
  (cond ((null? xs) #f)
        ((is-eq? x (car xs) #t))
        ((is-less? x (car xs)) #f)
        (else (element-of-sorted? x (cdr xs) is-eq? is-less?))))
